U+0670 Arabic Letter Superscript Alef

The Wikipedia has the following information about this codepoint:

The dagger alif (Arabic: ألف خنجرية alif khanjarīyah) or superscript alif is written as a short vertical stroke on top of an Arabic letter. It indicates a long /aː/ sound where alif is normally not written, e.g. هَٰذَا hādhā or رَحْمَٰن raḥmān. The dagger alif occurs in only a few modern words, but these include some common ones; it is seldom written, however, even in fully vocalised texts, except in the Qur'an. As Wright notes "[alif] was at first more rarely marked than the other long vowels, and hence it happens that, at a later period, after the invention of the vowel-points, it was indicated in some very common words merely by a fatḥa [i.e. the dagger alif.]" Most keyboards do not have dagger alif. The word الله (Allāh) is usually produced automatically by entering "alif lām lām hāʾ", or in Arabic: "ا ل ل ه". The word consists of alif + ligature of doubled lām with a shadda and a dagger alif above lām.